[PATCH] sanitize locate_fd()

* 'file' argument is unused; lose it.
* move setting flags from the caller (dupfd()) to locate_fd();
  pass cloexec flag as new argument.  Note that files_fdtable()
  that used to be in dupfd() isn't needed in the place in
  locate_fd() where the moved code ends up - we know that ->file_lock
  hadn't been dropped since the last time we calculated fdt because
  we can get there only if expand_files() returns 0 and it doesn't
  drop/reacquire in that case.
* move getting/dropping ->file_lock into locate_fd().  Now the caller
  doesn't need to do anything with files_struct *files anymore and
  we can move that inside locate_fd() as well, killing the
  struct files_struct * argument.

At that point locate_fd() is extremely similar to get_unused_fd_flags()
and the next patches will merge those two.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/fcntl.c b/fs/fcntl.c
index e632da7..3f3ac63 100644 (file)
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -55,14 +55,16 @@ static int get_close_on_exec(unsigned int fd)
  * file_lock held for write.
  */
 
-static int locate_fd(struct files_struct *files, 
-                           struct file *file, unsigned int orig_start)
+static int locate_fd(unsigned int orig_start, int cloexec)
 {
+       struct files_struct *files = current->files;
        unsigned int newfd;
        unsigned int start;
        int error;
        struct fdtable *fdt;
 
+       spin_lock(&files->file_lock);
+
        error = -EINVAL;
        if (orig_start >= current->signal->rlim[RLIMIT_NOFILE].rlim_cur)
                goto out;
@@ -97,42 +99,28 @@ repeat:
        if (error)
                goto repeat;
 
-       /*
-        * We reacquired files_lock, so we are safe as long as
-        * we reacquire the fdtable pointer and use it while holding
-        * the lock, no one can free it during that time.
-        */
        if (start <= files->next_fd)
                files->next_fd = newfd + 1;
 
+       FD_SET(newfd, fdt->open_fds);
+       if (cloexec)
+               FD_SET(newfd, fdt->close_on_exec);
+       else
+               FD_CLR(newfd, fdt->close_on_exec);
        error = newfd;
-       
+
 out:
+       spin_unlock(&files->file_lock);
        return error;
 }
 
 static int dupfd(struct file *file, unsigned int start, int cloexec)
 {
-       struct files_struct * files = current->files;
-       struct fdtable *fdt;
-       int fd;
-
-       spin_lock(&files->file_lock);
-       fd = locate_fd(files, file, start);
-       if (fd >= 0) {
-               /* locate_fd() may have expanded fdtable, load the ptr */
-               fdt = files_fdtable(files);
-               FD_SET(fd, fdt->open_fds);
-               if (cloexec)
-                       FD_SET(fd, fdt->close_on_exec);
-               else
-                       FD_CLR(fd, fdt->close_on_exec);
-               spin_unlock(&files->file_lock);
+       int fd = locate_fd(start, cloexec);
+       if (fd >= 0)
                fd_install(fd, file);
-       } else {
-               spin_unlock(&files->file_lock);
+       else
                fput(file);
-       }
 
        return fd;
 }